1. Field of the Invention
The invention relates to an apparatus and process for removing impurities, and more particularly, to an apparatus and process for removing fine impurities from a fibrous suspension.
2. Discussion of Background Information
Fibrous suspensions, particularly those obtained from recycled paper which are intended for paper production, contain undesirable attendant materials, also referred to as xe2x80x9cinterfering materials,xe2x80x9d which must be removed in the preparation system. The removal of these interfering materials is generally performed in various steps since a fibrous suspension purification in a single process step is rarely successful.
Wet straining processes have turned out to be particularly effective for the removal of fine impurities. In such processes, the suspension is conveyed into a straining device and is divided into at least two portions, an xe2x80x9cacceptsxe2x80x9d portion, i.e., the materials that have passed the wire, and a xe2x80x9crejectsxe2x80x9d portion, i.e., the materials rejected due to their size. Generally, in the parlance of paper makers, such wet straining processes are known as xe2x80x9csorting.xe2x80x9d It is also known to subject the rejected materials, i.e., the rejects portion, to one or more additional subsequent straining steps. This process is known as xe2x80x9cmultistep sorting.xe2x80x9d Multistep sorting can be carried out at various points of the paper stock preparation. Generally, the later the sorting occurs during the process, the finer the wire openings that can be used in the process. Examples of multistep wet straining are demonstrated in the scientific paper xe2x80x9cSortierung von Altpapierstoff zur Herstellung von graphischen Papierenxe2x80x9d [Sorting of Recycled Paper Stock for the Manufacturing of Graphic Papers] by R. Rienecker from the Wochenblatt fxc3xcr Papierfabrikation [Weekly for Paper Making] No. 23/24, 1997, pp. 1149 to 1159.
Although a large number of different systems are already known and used for purifying paper stock suspensions, these systems are often unsuccessful in removing all interfering impurities from the suspension. In particular, very fine, adhesive impurities, which often cause great difficulties in the production of paper, even in small quantities, can only be removed at great expense, if at all.
The present invention provides an apparatus and process for removing fine impurities from a fibrous suspension. The apparatus comprises a dissolution device, a pre-purification device, a wet straining device, and a flotation device. The wet straining device comprises at least two sorting devices installed in sequence, each sorting device having a wire for separating the fibrous suspension into an xe2x80x9cacceptsxe2x80x9d portion and a xe2x80x9crejectsxe2x80x9d portion. The flotation device is adapted to purify the xe2x80x9cacceptsxe2x80x9d portion of at least one sorting device, and further separates the fibrous suspension into an xe2x80x9cacceptsxe2x80x9d portion and a xe2x80x9crejectsxe2x80x9d portion.
The flotation device may be further adapted to purify the xe2x80x9cacceptsxe2x80x9d portion of the last of the at least two sorting devices. Additionally, the flotation device may be adapted to receive the xe2x80x9cacceptsxe2x80x9d portions of the last two of the at least two sorting devices.
The apparatus may also comprise a finishing device adapted to receive at least one xe2x80x9cacceptsxe2x80x9d portion of the wet straining device. Furthermore, the apparatus may be adapted to receive at least one xe2x80x9cacceptsxe2x80x9d portion of the flotation device.
The pre-purification device may be adapted to remove ink particles, and may remove these ink particles by flotation
Additionally, the sorting devices of the wet straining device may be embodied as closed pressure sorters. The pressure sorters may each be equipped with wires having free wire openings, the free wire openings having slits with a width of between about 0.08 and 0.5 mm. Alternatively, the free wire openings may be holes with a diameter of between about 0.8 and 3 mm.
The flotation device may additionally comprise a selectively functioning flotation cell.
The process for removing fine impurities from a fibrous suspension comprises the steps of subjecting the fibrous suspension to a dissolution process, subjecting the fibrous suspension to a pre-purification process, and purifying the fibrous suspension in a wet straining process. At the wet straining process, at least two sorting devices are installed in sequence, each sorting device having a wire for separating the fibrous suspension into an xe2x80x9cacceptsxe2x80x9d portion and a xe2x80x9crejectsxe2x80x9d portion. The wet straining process comprises introducing a xe2x80x9crejectsxe2x80x9d portion rejected at the wire of a preceding sorting device into the subsequent sorting device until a last subsequent sorting device has been reached, conveying the xe2x80x9crejectsxe2x80x9d portion out of the process, and conveying the xe2x80x9cacceptsxe2x80x9d portion to a flotation process. The xe2x80x9cacceptsxe2x80x9d portion is purified by at least one flotation process, which further separates the fibrous suspension into an xe2x80x9cacceptsxe2x80x9d portion and a xe2x80x9crejectsxe2x80x9d portion, the xe2x80x9crejectsxe2x80x9d portion containing a majority of the impurities of the fibrous suspension, and the xe2x80x9cacceptsxe2x80x9d portion containing a majority of the fibers of the fibrous suspension.
The xe2x80x9cacceptsxe2x80x9d portions of the sorting devices may contain the highest percentage of interfering materials that can be floated and may be purified in the flotation process.
Additionally, the xe2x80x9cacceptsxe2x80x9d portion of the last subsequent sorting device may be purified in the flotation process. Alternatively, the xe2x80x9cacceptsxe2x80x9d portions of the last two steps of the wet straining process may be supplied to the flotation step process.
The xe2x80x9cacceptsxe2x80x9d portions of the wet straining process that are not purified in the flotation process may also be combined and supplied directly to a finishing process. Also, the xe2x80x9cacceptsxe2x80x9d portion of the flotation process may be supplied to the remaining xe2x80x9cacceptsxe2x80x9d portions of the wet straining process.
The pre-purification process may remove ink particles, and may remove these ink particles by flotation.
The sorting devices of the wet straining process may be closed pressure sorters. These pressure sorters may be equipped with wires having free wire openings having slits with a width of between about 0.08 and 0.5 mm. Alternatively, the free wire openings may be holes with a diameter of between about 0.8 and 3 mm.
At the beginning of the wet straining process, the dry matter content of the fibrous suspension may be set to a value of between about 0.6 and 2.5%, or alternatively, may be set to a value of between about 2 and 4%.
The flotation step may be performed in a selectively functioning flotation cell.
The suspension to be purified may further contain adhesive particles.
Before the flotation step, the suspension may be subjected to a chemical treatment in which surface activity of the interfering materials is increased.
The fibrous suspension may be dispersed before the flotation process or alternatively, before the wet straining process. A specific work of at least 20 kWh/to may be transmitted to the fibrous suspension during the dispersion of the fibrous suspension.
The invention also provides for a process for removing fine impurities from a fibrous suspension, comprising conveying the fibrous suspension to at least one sorting device, separating the fibrous suspension using the at least one sorting device into an accepts portion and a rejects portion, finishing at least some of the accepts portion leaving the at least one sorting device using a finishing device, separating at least some portion of the rejects portion leaving the at least one sorting device using at least one last sorting device into an accepts portion and an rejects portion, separating at least some portion of the accepts portion leaving the at least one last sorting device into an accepts portion and a rejects portion using a flotation device, and finishing at least some portion of the accepts portion leaving the flotation device using the finishing device.
At least one intermediate sorting device may be arranged between the at least one sorting device and the at least one last sorting device, and the process may further comprise separating at least some of the rejects portion leaving the at least one sorting device using the at least one intermediate sorting device into an accepts portion and a rejects portion, and finishing at least some of the accepts portion leaving the at least one intermediate sorting device using the finishing device. The process may further comprise conveying at least some of the rejects portion leaving the at least one intermediate sorting device to the at least one last sorting device.
At least one intermediate sorting device may be arranged between the at least one sorting device and the at least one last sorting device and an additional flotation device, and the process may further comprise separating at least some of the rejects portion leaving the at least one sorting device using the at least one intermediate sorting device into an accepts portion and a rejects portion, separating at least some of the accepts portion leaving the at least one intermediate sorting device using the additional flotation device into an accepts portion and a rejects portion, and finishing at least some of the accepts portion leaving the additional flotation device using the finishing device. The process may further comprise conveying at least some of the rejects portion leaving the at least one intermediate sorting device to the at least one last sorting device.
At least a first and a second intermediate sorting device may be arranged between the at least one sorting device and the at least one last sorting device, and the process may further comprise separating at least some of the rejects portion leaving the at least one sorting device using the first intermediate sorting device into an accepts portion and a rejects portion, separating at least some of the accepts portion leaving the first intermediate sorting device using the second intermediate sorting device into an accepts portion and a rejects portion, and finishing at least some of the accepts portion leaving the second intermediate sorting device using the finishing device. The process may further comprise conveying at least some of the rejects portion leaving each of the first and second intermediate sorting devices to the at least one last sorting device.
An additional sorting device may be arranged after the at least one last sorting device, and the process may further comprise separating at least some of the rejects portion leaving the at least one last sorting device using the at least one additional sorting device into an accepts portion and a rejects portion, and conveying at least some of the accepts portion leaving the additional sorting device to the at least one last sorting device.
A first and a second intermediate sorting device may be arranged between the at least one sorting device and the at least one last sorting device and further comprising an additional sorting device arranged after the at least one last sorting device, and the process may further comprise separating at least some of the rejects portion leaving the at least one sorting device using the first intermediate sorting device into an accepts portion and a rejects portion, separating at least some of the accepts portion leaving the first intermediate sorting device using the second intermediate sorting device into an accepts portion and a rejects portion, separating at least some of the rejects portion leaving the at least one last sorting device using the additional sorting device into an accepts portion and a rejects portion, and finishing at least some of the accepts portion leaving the second intermediate sorting device using the finishing device. The process may further comprise conveying at least some of the accepts portion leaving the additional sorting device to the flotation device. The process may further comprise conveying at least some of the rejects portion leaving each of the first and second intermediate sorting devices to the at least one last sorting device.
Before the conveying of the fibrous suspension to at least one sorting device, the process may comprise subjecting the fibrous suspension to at least one of dissolution and pre-purification. Before the conveying of the fibrous suspension to at least one sorting device, the process may comprise subjecting the fibrous suspension to each of dissolution and pre-purification.
The process may further comprise removing ink particles during pre-purification. The ink particles may be removed by flotation during pre-purification. The flotation device may perform a flotation separation without chemicals. The flotation device may perform a flotation separation without chemicals used to remove inks. The flotation device may perform a flotation separation without flotation chemicals. At least one of the at least one sorting device and the at least one last sorting device may comprise a pressure sorter. The pressure sorter may be equipped with at least one wire. The at least one wire may have openings. The openings may comprise slits having a width of between about 0.08 and 0.5 mm. The openings may comprise holes having a diameter of between about 0.8 and 3 mm. A dry matter content of the fibrous suspension before entering the at least one sorting device may be between about 0.6 and 2.5%. A dry matter content of the fibrous suspension before entering the at least one sorting device may be between about 2 and 4%. The flotation device may comprise a selectively functioning flotation cell. The fibrous material suspension may comprise adhesive particles.
The process may further comprise chemically treating the fibrous material suspension in order to increase a surface activity of interfering materials, the chemical treatment occurring prior to the flotation device. Before the conveying of the fibrous suspension to at least one sorting device, the process may comprise subjecting the fibrous suspension to dispersion, and further comprising transmitting a specific work of at least 20 kWh/to to the fibrous suspension during the dispersion.
The invention further provides for an apparatus for removing fine impurities from a fibrous suspension, comprising at least one sorting device arranged to receive the fibrous suspension, the least one sorting device separates the fibrous suspension into an accepts portion and a rejects portion, a finishing device for finishing at least some of the accepts portion leaving the at least one sorting device, at least one last sorting device for separating at least some portion of the rejects portion leaving the at least one sorting device into an accepts portion and an rejects portion, and a flotation device for separating at least some portion of the accepts portion leaving the at least one last sorting device into an accepts portion and a rejects portion, wherein at least some portion of the accepts portion leaving the flotation device is subjected to finishing using the finishing device.
The apparatus may further comprise at least one intermediate sorting device arranged between the at least one sorting device and the at least one last sorting device, wherein at least some of the rejects portion leaving the at least one sorting device is separated using the at least one intermediate sorting device into an accepts portion and a rejects portion, and wherein at least some of the accepts portion leaving the at least one intermediate sorting device is subjected to finishing using the finishing device. At least some of the rejects portion leaving the at least one intermediate sorting device may be conveyed to the at least one last sorting device.
The apparatus may further comprise at least one intermediate sorting device arranged between the at least one sorting device and the at least one last sorting device and an additional flotation device, wherein at least some of the rejects portion leaving the at least one sorting device is separated using the at least one intermediate sorting device into an accepts portion and a rejects portion, wherein at least some of the accepts portion leaving the at least one intermediate sorting device is separated using the additional flotation device into an accepts portion and a rejects portion, and wherein at least some of the accepts portion leaving the additional flotation device is subjected to finishing using the finishing device. At least one of the rejects portion leaving the at least one intermediate sorting device may be conveyed to the at least one last sorting device.
The apparatus may further comprise at least a first and a second intermediate sorting device arranged between the at least one sorting device and the at least one last sorting device, wherein at least some of the rejects portion leaving the at least one sorting device is separated using the first intermediate sorting device into an accepts portion and a rejects portion, wherein at least some of the accepts portion leaving the first intermediate sorting device is separated using the second intermediate sorting device into an accepts portion and a rejects portion, and wherein at least some of the accepts portion leaving the second intermediate sorting device is subjected to finishing using the finishing device. At least some of the rejects portion leaving each of the first and second intermediate sorting devices may be conveyed to the at least one last sorting device.
The apparatus may further comprise an additional sorting device arranged after the at least one last sorting device, wherein at least some of the rejects portion leaving the at least one last sorting device is separates using the at least one additional sorting device into an accepts portion and a rejects portion, and wherein at least some of the accepts portion leaving the additional sorting device is conveyed to the at least one last sorting device.
The apparatus may further comprise a first and a second intermediate sorting device arranged between the at least one sorting device and the at least one last sorting device and further comprising an additional sorting device arranged after the at least one last sorting device, wherein at least some of the rejects portion leaving the at least one sorting device is separated using the first intermediate sorting device into an accepts portion and a rejects portion, wherein at least some of the accepts portion leaving the first intermediate sorting device is separated using the second intermediate sorting device into an accepts portion and a rejects portion, wherein at least some of the rejects portion leaving the at least one last sorting device is separated using the additional sorting device into an accepts portion and a rejects portion, and wherein at least some of the accepts portion leaving the second intermediate sorting device is subjected to finishing using the finishing device. At least some of the accepts portion leaving the additional sorting device may be conveyed to the flotation device. At least some of the rejects portion leaving each of the first and second intermediate sorting devices may be conveyed to the at least one last sorting device.
Before the fibrous suspension is conveyed to at least one sorting device, the fibrous suspension may be subjected to at least one of dissolution in a dissolution device and pre-purification in a pre-purification device. Before the fibrous suspension is conveyed to at least one sorting device, the fibrous material suspension may be subjected to each of dissolution and pre-purification.
Ink particles may be removed during pre-purification. The ink particles may be removed by flotation during pre-purification. The flotation device may perform a flotation separation without chemicals. The flotation device may perform a flotation separation without chemicals used to remove inks. The flotation device may perform a flotation separation without flotation chemicals. At least one of the at least one sorting device and the at least one last sorting device may comprise a pressure sorter. The pressure sorter may be equipped with at least one wire. The at least one wire may have openings. The openings may comprise slits having a width of between about 0.08 and 0.5 mm. The openings may comprise holes having a diameter of between about 0.8 and3 mm. A dry matter content of the fibrous suspension before entering the at least one sorting device may be between about 0.6 and 2.5%. A dry matter content of the fibrous suspension before entering the at least one sorting device may be between about 2 and 4%. The flotation device may comprise a selectively functioning flotation cell. The fibrous material suspension may comprise adhesive particles. The fibrous material suspension may be chemically treated in order to increase a surface activity of interfering materials, the chemical treatment occurring prior to the flotation device. Before the fibrous suspension is conveyed to at least one sorting device, the fibrous suspension may be subjected to dispersion, and wherein a specific work of at least 20 kWh/to is transmitted to the fibrous suspension during the dispersion.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.